<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"
	import="java.awt.*,java.awt.image.*,javax.imageio.*"%>
<%
	/*
	 使用方法：在需要显示验证码的html代码中使用<img uri='vcode.jsp'>
	 在需判断session的时候判断session.getAttribute("vcode")
	 */
	try
	{
		int height = 25;//验证码高度
		int codeLength = 4;//验证码长度
		int mixTimes = 5;//模糊程度参数
		Color bgColor = getRandColor(200, 250);//背景颜色
		Color bfColor = new Color(0, 0, 0);//字体颜色
		boolean ifRandomColor = true;//单个字符是否颜色随机
		boolean ifMixColor = true;//模糊线是否颜色随机

		//设置页面不缓存
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);
		// 在内存中创建图象
		int width = 13 * codeLength + 6;
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		// 获取图形上下文
		Graphics g = image.getGraphics();
		// 设定背景色
		g.setColor(bgColor);
		g.fillRect(0, 0, width, height);
		//设定字体
		g.setFont(new Font("Times New Roman", Font.PLAIN, 18));
		//画边框
		g.setColor(new Color(33, 66, 99));
		g.drawRect(0, 0, width - 1, height - 1);
		// 随机产生干扰线，使图象中的认证码不易被其它程序探测到
		g.setColor(getRandColor(160, 200));
		for (int i = 0; i < mixTimes * codeLength / 10; i++)
		{
			if (ifMixColor)
			{
				g.setColor(getRandColor(160, 200));
			}
			int x = random.nextInt(width);
			int y = random.nextInt(height);
			int xl = random.nextInt(12);
			int yl = random.nextInt(12);
			g.drawLine(x, y, x + xl, y + yl);
		}
		// 取随机产生的认证码(4位数字)
		String sRand = "";
		for (int i = 0; i < codeLength; i++)
		{
			String rand = String.valueOf(random.nextInt(10));
			sRand += rand;
			// 将认证码显示到图象中
			if (ifRandomColor)
				g.setColor(getRandColor(20, 110, 0));
			else
				g.setColor(bfColor);
			//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
			g.drawString(rand, 13 * i + 6, 16);
		}
		// 将认证码存入SESSION
		session.setAttribute("vcode", sRand);
		// 图象生效
		g.dispose();
		java.io.OutputStream os = response.getOutputStream();
		// 输出图象到页面
		ImageIO.write(image, "JPEG", os);
		os.flush();
		os.close();
		os = null;
		response.flushBuffer();
		out.clear();
		out = pageContext.pushBody();
	}
	catch (Exception e)
	{
		e.printStackTrace();
	}
%>
<%!//给定范围获得随机颜色
	private static Random random = new Random();

	private Color getRandColor(int fc, int bc)
	{
		return getRandColor(fc, bc, fc);
	}

	private Color getRandColor(int fc, int bc, int interval)
	{
		if (fc > 255)
		{
			fc = 255;
		}
		if (bc > 255)
		{
			bc = 255;
		}
		int r = fc + random.nextInt(bc - interval);
		int g = fc + random.nextInt(bc - interval);
		int b = fc + random.nextInt(bc - interval);
		return new Color(r, g, b);
	}%>